Method for electrostatic coating



A ril 12, 1966 HARUKICHI IWATA 3,245,328

METHOD FOR ELECTROSTATIC COATING Filed 001;. 23, 1962 FIG] INVENTOR.

BY W/ M 4 M PM,

United States Patent 3,245,828 METHOD FOR ELECTROSTATIC COATINGHarukichi Iwata, Tokyo, Japan, assignor to Iwata Tosoki Kogyo KabushikiKaisha, Tokyo, Japan Filed Oct. 23, 1962, Ser. No. 232,380 Claimspriority, application Japan, Jan. 31, 1962, 37/ 3,208 3 Claims. (Cl.117-934) This invention relates to a method for coatingelectrostatically a thing to be coated by using a common spray gun whichatomizes a coating material by compressed air.

A system of an electrostatic atomization coating was already proposed inthe past in which a coating material was mechanically atomized by a highliquid pressure, a centrifugal force, compressed air, etc.; an atomizedcoating material was injected into an electrostatic field; and a coatingwas carried out electr-ostatically by a potential difference providedbetween a spraying apparatus and a thing to be coated.

In an electrostatical coating, by using a common spray gun, a coatingeiliciency is very low because the energy held by an atomized particlesgroup is large and accordingly there is a great defect for practicaluse.

However, in using a common spray gun, there are many advantageous pointssuch asit is easy to handle in view of its far and wide spread; it iseasily possible to inject a coating material only when the thing to becoated appears just in front of a spraying apparatus by using anautomatic trigger device of a spray gun; and it is also possible tospray a coating material mechanically which is ditficult to spray byonly an electrostatic force.

Generally, the coating power of atomized particles of a coating materialunder the operation of an electrostatic voltage is very small contraryto our eXpectation, and, even if a speed held by sprayed particles islarger even by a very little, a coating efficiency is effected greatly.

The present invention improves the defects in the past 'by obtaining acomposite speed of atomized particles groups of a reduced speed byjetting and causing collision under a relatively low pressure from twospray guns located at symmetrical places at a proper angle which canreduce the speed of sprayed particles as a means of decreasing theenergy held by sprayed particles groups to be jetted.

It is understandable that a jetting energy from the two spray gunslocated at symmetrical places on a straight line is extinguished by thejetting of spray guns holding identical energies given from symmetricalplaces.

This invention is based on decreasing speed of injection from saidsymmetrical places, and the energy held by a sprayed particles groupafter collision caused by injection from the spray guns located atsymmetrical places on a straight line is the smallest, but a mist to beshaped cannot actually be advantageous for practical use.

Under the present invention, an oval-shape mist is obtained 'by givingspray guns which are located at symmetrical places, a proper angle bywhich the speed of sprayed'particles groups can be decreased.

This invention is characterized by decreasing the speed of sprayedparticles groups, and the injected atomized particles groups are furthersubdivided on the occasion they are made to collide with each other,and, as a result, fixing efliciency of a coating material is increased.As mentioned above, the speed of the mists which collide with each otherafter being injected from spray guns located at symmetrical places on astraight line becomes almost to be zero, and, from this fact, if thenearer the angles of injection of these two spray guns which make themists collide with each other are made to approach 3,245,828 PatentedApr. 12, 1966 'ice to a straight line, the slower the speed of thesemists becomes, and to the contrary, if the greater these angles areseparated, the faster the speed of these mists becomes; and if the angleof injection becomes smaller than 120, the speed of mists becomes largerthan that in the case of one spray gun. Therefore, the angle ofinjection should not be made smaller than 120.

The principal efficacy by this invention is, by using two commonautomatic spray guns, in coating very efficiently even dented faces,caved-in faces, etc. by having injected particles groups cross andcollide with each other and by preparing an oval spray particles groupof a slow speed.

Now the electrostatic coating method according to the present inventionwill be described with reference to the illustrated embodiments in theaccompanying drawing wherein,

FIG. 1 shows an electrostatic coating system which uses one embodimentof subject invention, and

FIG. 2 is a perspective View of a spraying apparatus excluding a thingto be coated.

In FIG. 1 and FIG. 2, the atomized particles groups injected fromautomatic spray guns 1 and 1 located at symmetrical places and supportedby stay 4 cross and are caused to collide with each other at cross angle2 which can reduce the speed of the sprays, the speed of the atomizedparticles group is reduced and they become an oval particles group andis coated on thing 5 to be coated. Cross angle 2 can be changed byadjusting butterfiy nuts 10 and 10, and better results can be obtainedby adjusting said cross angle 2 to a smaller one in the case the shapeof the thing to be coated is complicated, and in the case the shape ofthe thing to be coated is a relative-1y simple one, to a larger one.

Automatic spray guns 1 and 1' are ones commonly used, and compressed airenters from compressed air source 7 through air hoses 12 and 12' intocompressed air introduction holes 8 and 8; the opening and closing of aneedle valve of a spray gun is carried out and the starting and closingof injection can be carried out speedily by a cam device or anelectromagnetic device (not shown in the drawings). At the same time,compressed air is used for atomization of a paint; it is led fromcompressed air introduction holes 8 and 8 to air caps 13 and 13 at theend portion of said automatic spray guns and is injected from centralportions 11 and 11' and thereby the paint is atomized.

The pressure of the compressed air used for subject apparatus is notlimited under present invention, but tests show that it is within thescope of 0.5-1.5 kg./cm. and the quantity of the compressed air used isaround 1./min.

Automatic spray guns 1 and 1' are supported by stay 4; stay 4 is fixedto stand 9 and the fixing place of stay 4 can be changed up and down andthe height of injection can be adjusted freely. Of course, it ispossible to fix two or three sets of automatic spray guns to stand 9.

The paint which is divided into two directions from paint container 3,is led to said two spray guns 1 and 1 through paint hoses 14 and 14' andis injected from the spray guns 1 and 1 in the same quantity and itcollides with each other; but even in case the paint is led from onlyone hose, it is possible to practice the purpose of this invention.However, in this case, the quantity of paint to be injected is reducedin comparison with the quantity of air to be injected, and preferableresults cannot 'be obtained, resulting in a drop of an atomizationefficiency. Therefore, the paint should be injected in the samequantities from the two spray guns 1 and 1'.

According to the shape of the thing to be coated, it is necessary toadjust the quantity of the paint to be injected and a pattern form ofmist, and the quantity of 3 paint to be injected can be adjusted simplyby turning paint adjusting knobs 15 and 15'.

A pattern shape can be changed by changing a cross angle or spray airpressure, or by exchanging an injection nozzle.

A pole of stand 9 is made of an insulating material, and electricitywhich is generated from high voltage generator 6 is transmitted to stay4 which is made of an electricity conducting material and automaticspray guns 1 and 1', and atomized particles are injected in anelectrostatic field formed between a spraying mechanism and thing to becoated 5 which is grounded, and coated electrostatically on thing to becoated 5 by the operation of an electrical field.

Under the present invention, it is possible to carry out anelectrostatic coating of good coating efliciency in which dented facesand caved-in faces are well coated, by preparing an electrostaticcoating apparatus which can be practically used rather simply byemploying two automatic spray guns which are commonly used.

What is claimed is:

1. A method of electrostatically coating an object by means of a streamof compressed gas atomized coating material directed generally toward anobject to be coated, comprising directing two separate substantiallyequal streams of compressed gas atomized coating material toward andagainst each other from two spaced locations symmetrically disposed onopposite sides of a plane extending from the object to be coated andbetween said spaced locations, said separate streams being at equalangles to said plane and being at an angle to each other which is from180 to as measured on the sides of the streams remote from the object tobe coated, and while directing said streams, maintaining anelectrostatic field between the object and the said spaced locations,whereby the colliding separate streams are combined into said streamdirected generally toward the object and said stream moves toward theobject with a velocity from a velocity equal to the velocity of theseparate streams to a velocity imposed solely by the electrostaticfield.

2. A method as claimed in claim 1 in which automatic spray guns are usedas the sources of the separate streams of atomized coating material, andthe step of maintaining the electrostatic field comprises insulating thespray guns from support means therefor charging a high voltage on saidspray guns, and grounding the object to be coated.

3. A method as claimed in claim 2 in which the automatic spray guns areadjustably mounted on the supports therefor, whereby the angle betweenthe separate streams can be varied.

References Cited by the Examiner UNITED STATES PATENTS 2,428,991 10/1947 Ransburg 11793.4

JOSEPH B. SPENCER, Primary Examiner.

RICHARD D. NEVIUS, Examiner.

1. A METHOD OF ELECTROSTATICALLY COATING AN OBJECT BY MEANS OF A STREAMOF COMPRESSED GAS ATOMIZED COATING MATERIAL DIRECTED GENERALLY TOWARD ANOBJECT TO BE COATED, COMPRISING DIRECTING TWO SEPARATE SUBSTANTIALLYEQUAL STREAM OF COMPRESSED GAS ATOMIZED COATING MATERIAL TOWARD ANDAGAINST EACH OTHER FROM TWO SPACED LOCATIONS SYMMETRICALLY DISPOSED ONOPPOSITE SIDES OF A PLANE EXTENDING FROM THE OBJECT TO BE COATED ANDBETWEEN SAID SPACED LOCATIONS, SAID SEPARATE STREAMS BEING AT EQUALANGLES TO SAID PLANE AND BEING AT AN ANGLE TO EACH OTHER WHICH IS FROM180* TO 120* AS MEASURED ON THE SIDES OF THE STREAMS REMOTE FROM THEOBJECT TO BE COATED, AND WHILE DIRECTING SAID STREAMS, MAINTAINING ANELECTROSTATIC FIELD BETWEEN THE OBJECT AND THE SAID SPACED LOCATIONS,WHEREBY THE COLLIDING SEPARATE STREAMS ARE COMBINED INTO SAID STREAMDIRECTED GENERALLY TOWARD THE OBJECT AND SAID STREAM DIRECTED GENERALLYTOWARD THE OBJECT AND SAID STREAM MOVES TOWARD THE OBJECT WITH AVELOCITY FROM A VELOCITY EQUAL TO THE VELOCITY OF THE SEPARATE STREAMSTO A VELOCITY IMPOSED SOLELY BY THE ELECTROSTATIC FIELD.